The present invention relates generally to digital communications systems, and more specifically to an architecture of a scalable bandwidth single-stage digital cross-connect switching system.
Digital communications systems are known that employ digital cross-connect switching systems for cross-connection of high speed optical or electrical signals in broadband communications networks. An architecture of a conventional digital cross-connect switching system includes a plurality of input ports, a plurality of output ports, a cross-connect such as a Time Division Multiplex (TDM) cross-connect, and at least one connection memory. The TDM cross-connect is typically configured to connect any input port with any one or more of the output ports based on connection information stored in the connection memory. For example, high speed optical or electrical signals received by the TDM cross-connect may comprise a plurality of data frames contained in a number of respective time slots. Further, the TDM cross-connect may temporarily store the data received at one of the input ports during a first time slot, and may subsequently retransmit that data during a second time slot, which is assigned to at least one of the output ports. The TDM cross-connect accesses the connection information pertaining to the respective time slot/output port assignments from the connection memory.
Various techniques are known for increasing the bandwidth of conventional digital cross-connect switching systems. For example, the TDM cross-connect may be employed in a Synchronous Optical NETwork (SONET) multiplexed communications system. According to the SONET standard, high speed optical or electrical signals are generally formatted in Synchronous Transport Signal (STS) frames. A basic STS-1 frame comprises nine rows of data bytes by ninety columns of data bytes, in which the first three columns contain Transport OverHead (TOH) bytes and the remaining eighty-seven columns contain Synchronous Payload Envelope (SPE) bytes. In order to increase the bandwidth of the TDM cross-connect in the SONET communication system, M (M>1) STS-1 tributaries may be multiplexed together to form a single STS-M frame by interleaving the STS-1 tributaries one byte at a time (“byte interleaving”). Alternatively, the bandwidth of the TDM cross-connect may be increased by interleaving the STS-1 tributaries one bit at a time (“bit interleaving”) or one column at a time (“column interleaving”).
However, such conventional techniques for increasing the bandwidth of digital cross-connect switching systems have drawbacks. For example, the first row of a typical STS-1 frame includes TOH bytes A1 and A2, which form a framing pattern of bits indicative of the start of the frame. When performing byte, bit, or column interleaving on STS-1 tributaries, these framing bits are frequently lost, thereby requiring the cross-connect switching system to generate new framing bits for the interleaved data. Further, the bit interleaving technique normally cannot increase the bandwidth of the TDM cross-connect by more than a factor of 8. Moreover, an increased amount of connection information is typically needed for properly routing the interleaved bits/bytes/columns of data to the desired output port(s), thereby requiring use of a significantly larger connection memory.
It would therefore be desirable to have an architecture of a digital cross-connect switching system that has a scalable bandwidth. Such a cross-connect switching system would employ a connection memory that is smaller than that used in conventional high bandwidth cross-connect switching systems. It would also be desirable to have a scalable bandwidth digital cross-connect switching system that has a single-stage architecture.